We propose a systematic collaborative program of coordinated ultrastructural and biochemical research design to elucidate the mechanisms which determine and regulate the secretion of adenohypophysial growth hormone and prolactin. The morphologic aspects of this research will focus special effort on the electron microscopic immunocytochemistry of the hormones involved, both in tissue studies and in isolated subcellular fractions. Attention will be directed to the isolation, identification, and characterization of pituitary microfilaments and their possible relatedness to actomyosin or other contractile proteins as well as their potential role in hormonal secretion. The biochemical composition and enzymatic activities of isolated secretory granules and their membranes will be studied by standard chromatographic and electrophoretic techniques, combined with radioimmunoassay determinations of the hormones. The mode of hormonal packaging and the potential role in secretion of granule membrane enzymes will be examined. Combined biochemical, ultrastructural, and dynamic secretory studies will be carried out on pituitary glands during the induction of neoplastic change under the influence of estrogens, and on human pituitary tumors.